In the case of 'problems'... tackle - start finding strategies to (hopefully) deal with the problem + probably reduce the impact of the problem cope with - accepting that the problem exists and finding ways to live with it + possibly looking for solutions fix - same as 'solve' but more informal style solve - finding solutions to a problem that will eliminate it.

In addition to what Charlie said; they have the following connotations or valence: Tackle: this has positive connotation, i.e. to approach it like a challenge to be solved. Cope with: this has a more negative connotation, i.e. it is a negative situation and you must accept it, cope with it, endure it, etc. Fix: neutral connotation, may be more relevant to less abstract, more tangible problems, i.e. fixing mechanical problem, fixing a physical system, etc. Usually used when something is broken and it previously worked/functioned properly. Solve: neutral connotation, more applicable to more abstract problems. Compared to 'fix,' it may be the first time this solution has been solved/found, at least by you...i.e. like solving a math problem.